In mass spectrometry apparatuses, ion traps having high sensitive characteristics have been widely employed. Among these ion traps, since ion amounts which can be trapped at once (trapping capacities) into linear ion traps constructed of 4 pieces of rod electrodes are large, as compared with those of conventional three-dimensional traps (on the order of 1,000 to 10,000 pieces), the linear ion traps can perform high-sensitivity analyses and have been widely employed.
Patent Literature 1 describes a method for mass-selectively ejecting ions of a specific mass along an axial direction of a rod set, which are resonant-excited along a radial direction within a linear ion trap, by utilizing the fringing fields generated at ends of the rods after the ions have been accumulated in the linear ion trap.
Patent Literature 2 describes the following method; after ions have been accumulated in a linear ion trap, DC voltages are applied to electrodes inserted between rod electrodes so as to form a harmonic potential on a center axis. Ions of a specific mass which are resonant-excited along an axial direction within this harmonic potential on the center axis are mass-selectively ejected along the axial direction of the rods.
Patent Literature 3 describes a method for mass-selectively ejecting ions of a specific mass along an axial direction of the rod electrodes, which are resonant-excited along a radial direction within a linear ion trap, by utilizing a DC voltage applied between wire electrodes inserted between the rod electrodes after the ions have been accumulated in the linear ion trap.
Patent Literature 4 describes several methods capable of producing electric fields along axial directions of rod electrodes. For instance, the electric fields can be produced on the center axes by employing taper-shaped rod electrodes, employing rods which are not parallel to each other, employing rods having resistivities as the rod electrodes, or employing other electrodes between the rod electrodes, so that a potential for moving ions along the axial directions can be formed.
Furthermore, Patent Literature 1 describes that by adding these methods described in Patent Literature 4, ions are converged to a specific portion on the center axis and the ejection efficiency of the ions is increased.
Patent Literature 5 describes that vane electrodes whose distances from a center axis vary along axial positions are inserted among the respective rod electrodes which constitute a linear ion trap and collision-induced dissociation of the ions is performed. There is described that with employment of this collision-induced dissociation, even when buffer gas pressure is low, the dissociation is more effectively progressed.